1. Technical Field of the Invention
This invention relates to telecommunication systems and, more particularly, to a generic call server and method of converting signaling protocols that utilizes a Generic Call-control State Machine (GCSM) for handling call-control signaling between a plurality of different signaling systems.
2. Description of Related Art
It is anticipated that telecommunications networks will be hybrid networks containing both second generation (2G) and third generation (3G) components and areas of service for years to come. In a typical hybrid network, a number of different signaling protocols may be utilized including, for example, the Internet Protocol (IP), the International Telecommunications Union—Telecommunications Standardization Sector (ITU-T) H.323 and H.248 protocols, the Internet Engineering Task Force (IETF) Session Initiation Protocol (SIP), the Mobile Application Part (MAP), the ANSI-41 Intersystem Signaling protocol, the Signal System 7 (SS7) protocol, the Integrated Services Digital Network (ISDN) User Part (ISUP) protocol, and the Bearer Independent Call Control (BICC) protocol, an extension of ISUP.
An analysis of various call cases, performed for different combinations of networks and different types of subscribers, results in the functional block diagram illustrated in FIG. 1. This diagram illustrates the call-control functional components that are required in a hybrid network 10 in order to handle the various combinations of signaling systems that are currently utilized. Extensions to protocols are indicated by a “+” sign. Block 11 represents the functionality required for a call-control handler that is capable of handling all combinations of the existing signaling protocols. The handler is functionally divided into a plurality of servers and a plurality of media gateway controllers (MGCs). Several types of servers exist. The different types of servers can be grouped into the following four groups:                Servers that understand only one type of protocol. These servers provide subscriber services. They do not control a media gateway (MGW), and therefore have no MGC functionality. These are illustrated in FIG. 1 as blocks 12 and 13.        Servers that map between different types of protocols in order to bridge different transport schemes such as packet-switched and circuit-switched transport schemes. Therefore, they control an MGW using the H.248 protocol. These servers do not provide any subscriber services. Within block 11, these servers are identified as Media Gateway Control Functions (MGCFs). These are illustrated in FIG. 1 as blocks 16 and 18.        Servers that map between different types of protocols in order to bridge different transport schemes, and provide subscriber services as well. The subscriber services are provided either by using internal logic or by interacting with other nodes located in the service control plane. Within block 11, these servers are identified as a Mobile Switching Center (MSC) server 14 and as Gateway MSC (GMSC)/MGCFs 19–21, 22–23, and 24–25.        Servers that map between different protocols operating on identical transport schemes. These servers do not control an MGW, and therefore have no MGC functionality. This type of server is illustrated in FIG. 1 as block 26.        
A SIP server 12 is needed to handle SIP signaling in a pure SIP network; an H.323 gatekeeper (GK) 13 is needed to handle H.323 signaling in a pure H.323 network; and an MSC server 14 is needed to handle BICC, H.248, and Iu2 interface signaling for Universal Mobile Telecommunication System (UMTS) and IS-136 Time Division Multiple Access (TDMA) networks. The MSC server also handles MAP, ANSI-41, and IP signaling with a Roaming Signaling Gateway (R-SGW) 15. The R-SGW converts SS7 to IP for ANSI-41 (mobile) call cases. The MSC server is used within the context of TDMA networks, Global System for Mobile Communications (GSM) networks having an IP transport scheme, and UMTS circuit-switched networks.
Several types of MGCFs are required in the call-control handler. In addition to call control, the main functions performed by the MGCFs are call-control protocol conversion and media gateway control using the H.248 protocol. Six MGCFs are illustrated to show the different types of protocol conversions required of an MGCF for different call scenarios.
A first MGCF (MGCF-1) 16 is needed to handle H.323 and H.248 signaling, as well as ISUP/IP signaling toward a Transit Signaling Gateway (T-SGW) 17. The T-SGW converts SS7 to IP for ISUP (non-roaming) call cases. A second MGCF (MGCF-2) 18 is needed to handle SIP and H.248 signaling, as well as ISUP/IP signaling toward the T-SGW. A third MGCF (MGCF-3) 19 interconnects an external network utilizing SS7 signaling to the circuit-switched portion of a 3G core network. Therefore, MGCF-3 is needed to handle BICC signaling toward the circuit-switched domain, H.248 signaling, and ISUP/IP signaling toward the T-SGW. MGCF-3 should be functionally combined with a Gateway MSC (G-MSC) 21 functionality which handles a subset of MAP, ANSI-41, and IP signaling for HLR interrogations. MGCF-3 performs all the MGC-specific functionalities: protocol conversion, address translation, bandwidth reservation and Media Gateway (MGW) control. The G-MSC is used only for incoming traffic into a home network, when the HLR interrogation is necessary to find a subscriber's location.
A fourth MGCF (MGCF-4) 22 interconnects H.323 networks to the circuit-switched portion of a 3G core network and is needed to handle BICC signaling toward the circuit-switched domain of the 3G core network, H.248 signaling, and H.323 signaling. Once again, MGCFs handling BICC signaling should be functionally combined with a G-MSC 23 that performs HLR interrogations. A fifth MGCF (MGCF-5) 24 interconnects SIP networks to the circuit-switched portion of a 3G core network and is needed to handle BICC signaling toward the circuit-switched domain of the 3G core network, H.248 signaling, and SIP signaling. Once again, MGCF 5 should be functionally combined with a G-MSC 25 that performs HLR interrogations. A sixth MGCF (MGCF-6) 26 is needed to handle SIP and H.323 signaling.
Communications such as interrogations 27 of Domain Name Servers (DNS) and Location Servers (LS) are common to all of the signaling systems. Likewise, each of the signaling systems is capable of utilizing the Bandwidth Broker protocol 28 with a bandwidth broker performing resource management (RM) functions for the purpose of coordinating Quality of Service (QoS) in IP networks.
Each of the protocols utilized by the various signaling systems have protocol-specific functionality. This creates a major problem for manufacturers of equipment such as media gateway controllers because different versions of the controllers must be designed for each unique set of protocols. Alternatively, to provide a single device in the network that is capable of converting between all of the specific protocols, with all of the protocol-specific functionality, would require an extremely large matrix of great complexity.
It would be advantageous to have a generic call server and method of converting protocols that simplifies the protocol conversion problem and handles call-control signaling between a plurality of different signaling systems. Such a server would enable equipment manufacturers to design a single version of devices such as media gateway controllers that would be compatible with a plurality of signaling protocols. The present invention provides such a generic call server and method.